House construction on narrow land? 3-family house already exists

I don't know if that is possible without further measures. Basically, I would first say no, because all the windows would have to be removed and some rooms wouldn't get any daylight at all.

So I just checked again. 2 houses in the immediate vicinity (2-3 houses next door) actually have houses as rear development. I hope that this way I can argue with the BA

Look at the development plan that is relevant for you.

The blue lines mark the current building windows. As you can see, the actual development on some plots deviates from this, which indicates that the development is older than the development plan from 1968. The deviations can therefore very likely be explained by Grandfather protection, which can be seen, for example, on plots 679 and 680, which you are probably referring to, because border distances etc. are not observed there. Under today's planning law, you probably would no longer get approval there.

The same even applies to your plot – your house extends out of the building window to the north (which is somewhat odd, since according to your information the house was only built in 1972, i.e. 4 years after the development plan was established). If you were to demolish your house, you would not be allowed to rebuild it in the same place but would have to adhere to the building window in the standard case and move the house southwards.

Well, asking doesn't cost anything in the end, but I see better chances in bundling all owners together and making densification of developed areas appealing to the city planners.

When arguing, it doesn't hurt to think like a city planner: if they gave you a building permit that is only very, very slightly legally contestable, they would have the corresponding lawsuit on the table faster than you can spell your name. They have no interest in that – it only costs money, nerves, and brings in nothing.

Therefore, all neighbors/owners must first be convinced that this is a cool idea. If that is the case, the effort is worth it for the city – otherwise not.

Best regards Dirk Grafe

In case that really a consent of the neighbors is required, I see no chance.

IMHO .. if you don't get your neighbors on board, you can kiss the building plans goodbye.

The hope has meanwhile also faded. However, I have another question/thought.

The lower apartment in the 3-family complex is on the ground floor. The basement is a souterrain and there is the possibility to access the 3 cellar rooms from the stairwell.

My question is: Is it fundamentally possible to have a staircase built from the lower apartment that leads directly into the basement? One would basically turn it into a maisonette apartment. Because the cellar rooms are very well maintained and also habitable. I imagine the whole thing to be complicated and difficult, but is there theoretically this possibility?

Regards

On the one hand, I assume that these are concrete ceilings/floors. You cannot afterwards install a stairwell opening there. If it is wood, then it is more likely. However, you probably have to consider the matter from a structural perspective as well.

However:

Denn die Kellerräume sind sehr gepflegt und auch bewohnbar.

these will be basement rooms, not habitable rooms with appropriate ceiling height, nor a second escape route, nor adequate lighting (well-maintained basement rooms are not equivalent to habitable rooms). Search for "habitable room" on Wiki, and you'll get an idea of what it means. So you cannot simply convert a basement room into a bedroom.

Edit: But perhaps your basement meets all the requirements? I overlooked the word Souterrain.